rt2x00: Remove unneeded variable

The update_bssid is set only when BSS_CHANGED_BSSID is used,
but the check if that field is true is done later in the function
but also only when BSS_CHANGED_BSSID is set. This makes the
variable useless, as it can never result in a negative check.

Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Acked-by: Helmut Schaa <helmut.schaa@googlemail.com>
Acked-by: Gertjan van Wingerde <gwingerde@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>